1. Field of the Invention
This invention relates to the art of producing elongated hollow articles from thermoplastic material, and is more particularly concerned with draw-molding such articles from stretchable thermoplastic sheet or film material.
2. Description of the Prior Art
Difficulty has heretofore been experienced in producing elongated articles of large length to diameter ratios from thermoplastic material, and more particularly from stretchable thermoplastic material. Especially difficult has been the attainment of desired wall thicknesses, whether such thicknesses should be uniform or of differential thickness in different areas of the wall. Wall design and quality control have been hampered.
During long length to diameter draws, the thermoplastic material tends to stretch excessively or unevenly in elongated wall portions of the hollow articles.
Thin liners of thermoplastic material (which may be multi-layered) are desirable for use in making multi-walled flow molded containers. These liners need to be produced with great uniformity with a desirable distribution of wall material within the individual liners. Liner thicknesses, from liner to liner, can vary, depending upon end use properties desired, as is appreciated in this art.